Aerial refueling of a receiver aircraft from a tanker aircraft is commonly performed. Nevertheless, aerial refueling is a difficult and dangerous maneuver that is typically attempted only by military personnel throughout the world. Today, usually two types of aerial refueling systems are used: extendable boom systems and hose-and-drogue systems.
In a hose-and-drogue system, the drogue is attached to the outlet end of a hose. The inlet end of the hose is attached to a hose reel onto which the hose is wound. The hose reel is typically mounted either within a tanker aircraft fuselage or on a refueling pod or module which is attached to the bottom of the tanker aircraft. The hose reel is commonly connected to a motor and/or pump that is hydraulically driven. The hydraulic motor-pump can be connected through a coupling system, which may include, e.g., various gear boxes, shafts, and couplings. When the hose is deployed from the tanker aircraft, the drogue encounters drag and the hose reel rotates in a trail direction in which the hose extends behind the tanker aircraft.
When the hose and the drogue are fully extended, a pilot of a receiver aircraft maneuvers the receiver aircraft to engage a refueling probe of the receiver aircraft with the drogue. Danger arises because the high speeds of the tanker and receiver aircrafts relative to the ground and to each other can result in the drogue being hit with considerable force during engagement. Such engagements may create slack in the hose that must be quickly eliminated. Otherwise, the risk of aircraft accidents increases substantially. Retracting the hose onto the hose reel eliminates the slack.
After the drogue is engaged, fuel can be pumped from the tanker aircraft to the receiver aircraft. When refueling is complete, the pilot of the receiver aircraft disengages the refueling probe from the drogue. When the receiver aircraft tries to disengage within the refueling range, it is referred to as “flowing disconnect”, and pulling forces on the hose can increase significantly. The hose can then be retracted onto the hose reel for storage by rotating the hose reel in a retract direction.
Thus, the hydraulic motor-pump operates in a pump mode to rotate the hose reel in a trail direction and to extend the hose. Conversely, the hydraulic motor-pump operates in a motor mode to rotate the hose reel in the retract direction and to retract the hose onto the hose reel. In the trail mode, hose position can be controlled independently from variations in hose tension. In the retract mode, hose tension can be controlled independently from variations in hose position.
Aerial refueling systems have utilized hydraulic motor-pumps incorporating fixed displacement hydraulic motors that control the extension of the hose in a pump mode and control the retraction of the hose in a motor mode. However, such systems suffer from low hose retraction rates and accessory components that increase overall weight and response time of the system. Information relevant to attempts to address these problems can be found in U.S. Pat. Nos. 6,454,212 and 6,866,228, which disclose variable displacement hydraulic motor-controlled hose reel drive systems.